Depression is common and disabling. Advances in telecommunications have greatly increased the possibilities for delivering behavioral interventions. Unfortunately, the initial results in this emerging field indicate that much work remains before viable systems can be implemented clinically. The mission of this Center is to develop and pilot novel systems of care that can provide efficacious, scalable, cost-effective, patient friendly technology assisted behavioral interventions (TABIs) for the treatment and prevention of depression. The Center's model proposes that adherence and efficacy can be enhanced by increasing support from humans, creating greater connectedness to patients in their environments, and developing new interfaces that are more conducive to promoting complex behavior change. To this end, we will propose a Technology Development Unit that will develop and refine three new technologies that address each of these areas, two pilot trials that will test novel interventions in the treatment and prevention of depression, and two measurement projects that will develop and evaluate metrics. The Technology Development Unit will 1) refine mobile phone technology that can continuously monitor patient behavior, environmental context, and mood, and can reach out to engage the patient at critical moments in his/her environment, 2) refine an online peer network that is specifically designed to activate participants to provide support and encourage accountability among its members, and 3) develop programmable virtual humans to support interpersonal skills training. Two pilot trials will 1) evaluate these technologies in the context of an internet treatment for depression in adults and 2) evaluate these technologies in the context of an internet treatment for prevention of depression in adolescents. Measurement projects will, using data collected in the pilot trials, evaluate measurement in two critical areas for TABIs: adherence and cost-effectiveness.